The prevalence of COPD approaches 22% of the Veteran population, and patients with severe COPD experience an average of 2.5 exacerbations per year. COPD exacerbations can be triggered by both bacterial and viral respiratory infections, however increasing evidence suggests that air pollution is also a cause. Prior studies examining the relationship between air pollution and hospitalization rates have been ecologic studies at the city level, and have not controlled for patient-level characteristics such as disease severity, and focused only on the most severe exacerbations that lead to hospitalizations. Few studies have evaluated the relationship between outdoor ambient air pollution and important COPD outcomes such as chronic symptoms, health- related quality of life or physical activity. The overall purpose of this study is to examine the impact of outdoor air pollution on risk of exacerbations, health related quality of life and physical function among patients with COPD. Specific aims: The goal of this proposal are to: 1) examine whether chronic exposure to outdoor air pollution is associated with exacerbations and respiratory symptoms among COPD patients, and 2) determine whether outdoor air pollution is associated with worse COPD-specific health-related quality of life and decreased physical activity. Methods: We propose an additional year of follow-up for COPD patients currently enrolled in VA CSP #560 (BREATH), a multicenter randomized clinical trial of a comprehensive self-management intervention that enrolled 425 patients. The study is currently in observational phase set to end September 30, 2010. The proposed research is an opportunity to continue to follow this unique and well-characterized population with moderate to severe COPD in order to collect additional data on patient exacerbations, physical activity, and HRQOL. Patient-level data will be linked to air pollution data and data regarding the built environment including walk ability and time spent outdoors. Previously assessed information on COPD symptoms/outcomes and HRQOL will be combined with an additional year of measurements on patients' COPD symptoms/outcomes, HRQOL, physical activity, air pollution, and built environment. Mixed effects Poisson regression models will be employed to examine the associations between (1) air pollution and exacerbations rates and the interaction between pollution and the built environment, and (2) air pollution and COPD-specific and general HRQOL as well as physical activity. Models will be adjusted for important covariates including socioeconomic status and COPD disease severity. Conclusions: The results of the proposed study will greatly advance our understanding of the impact of ambient air pollution on exacerbations, HRQOL and PA. The results will provide data to counsel patients, improve self-management programs and to better develop interventions to increase physical activity and improve quality of life in COPD.